In general, in a process of manufacturing a flat panel display (FPD) such as a semiconductor, a liquid crystal display (LCD), or an organic liquid emitting diode (OLED), an air-blowing process is used to remove foreign materials such as particles occurring from a surrounding environment.
For example, in an automated optical inspection (AOI), which is a final step of a process of manufacturing the LCD display, since an object to be inspected is recognized as defective even if only one floating particle is placed on the object to be inspected, there is a need for a process of blowing a surface of the object to be inspected using air immediately before the automated optical inspection in order not to lower an inspection yield.
However, since a pixel size of a display recently continues to be reduced as compared with a conventional air-blowing cleaning technology in which particles of 10 μm or less are not removed, a dry cleaning technology having stronger cleaning power than the air-blowing cleaning technology is required.
The most representative dry cleaning technology is a dry ice snow spray type cleaning technology, and a cleaning technology of spraying sublimable dry ice particles (snow) formed by a phase change of liquid carbon dioxide onto the surface of the object to be cleaned and removing foreign materials such as particles by collision energy occurring at the time of the spraying has been proposed in U.S. Pat. No. 5,125,979.
In general, in a case in which the dry ice snow spray type cleaning technology is applied to an object having a solid surface such as a metal or a ceramic, since hardness of the dry ice is about 2.5 based on the Mohs hardness testing machine, there is little possibility of damaging the surface of the object, but since the surface of the object used in the process of manufacturing the semiconductor or the display is often very soft and is very sensitive to a small change due to characteristics of the material, the application of the dry ice snow spray type cleaning technology is very limited in a case in which the surface of the object to be cleaned is not completely prevented from being damaged.
Typically, in the application of the dry ice snow spray type cleaning technology, the cause of the damage to the surface of the object to be cleaned is because an impulse is increased due to a mass effect of particles when large dry ice particles which are irregularly grown collide with the surface of the object to be cleaned.
A mechanism in which the growth of the dry ice particle occurs will be described below. In a case in which a speed of liquid carbon dioxide is slowed down inside the liquid carbon dioxide nozzle after dry ice seed particles (snow) are generated, the dry ice particles around the liquid carbon dioxide nozzle are aggregated into one particle and the growth of the dry ice particles occurs.
Further, if the dry ice particles are adsorbed on a surface of an end of the liquid carbon dioxide nozzle, the growth of the dry ice particles instantaneously progress rapidly, and the large dry ice particles which are rapidly grown as described above become larger in mass and damage the surface of the object to be cleaned.
Therefore, in order to suppress the growth of the dry ice particles at most, it is most important to minimize a distance that liquid carbon dioxide moves within the liquid carbon dioxide and to thin a thickness of the end of the liquid carbon dioxide nozzle at most to prevent adsorption and growth of the dry ice particles around the liquid carbon dioxide nozzle.
Meanwhile, since the display has recently been increased in size, an area to be cleaned is also increased and there is a limitation that it is difficult to shorten a cleaning time using a conventional single nozzle.
In order to apply the cleaning technology to a large area of the object to be cleaned due to the increase in size, a wide nozzle type is required, but in a case in which the wide nozzle is formed by simply arranging nozzles in parallel to each other, there is a problem that consumption of liquid carbon dioxide (CO2) is too large and economics are significantly decreased.